I have the circuit below based on a simple 555 timer generating a PWM signal to dim an LED. The LED is lit but the brightness doesn't change as you would expect by adjusting the pot. Changing the potentiometer has no effect on the LED. Another thing I noticed, I cannot see the PWM waveform on the scope it just looks like a stable voltage. This circuit works fine in real life on a breadboard. Is there something obvious I'm missing? Thanks. I copied the schematic from this article: https://www.electronicshub.org/555-timer-pwm/